Conventionally, a liquid crystal display is formed with a spacer dispersed and interposed between two sheets of material comprising a transparent electrode and a crystal oriented layer to form a predetermined space into which a liquid crystal is injected. Thereafter, a polarizing panel is attached to the outer surface of a substrate. Despite the complex fabrication process, response speed and contrast of the display region is not good. Moreover, with the limited display region, it is impossible to form large area displays.
A PDLCD (polymer dispersed liquid crystal display) which can be simply fabricated and is suitable for making very large display area was introduced by a report of American Institute of Physics published in 1986 as NCAP (nematic curvilinear aligned phase). The PDLCD described therein consists of nematic liquid crystal dispersed in a polymer film in the shape of droplet. Light passing through the film in the absence of an applied electric field is intercepted, giving an opaque film. Application of an electric field across the liquid crystal/polymer places the film in a highly transparent state. The PDLCD technology possesses many advantages in comparison with other liquid crystal technologies. One of the great advantages is the ability to make large liquid crystal devices, potentially square meters in size, since the polymer protects nematic liquid crystals from the environment. There is no need of forming an oriented layer in the substrate, as the polymer defines the alignment of the contained liquid crystal. In addition, polarizers need not be used by using polymer whose refractive index is similar to that of liquid crystals.
The processes used in constructing the PDLCD are quite simple. The simplest method consists of the steps such that, a nematic liquid crystal is dispersed in a water-borne polymer to form an emulsion, the emulsion is applied as a coating onto a conductive transparent substrate, such as indium tin oxide (ITO) coated polymer, and film is allowed to dry, and then laminated to another piece of conductive substrate to give a finished cell.
However, the PDLCD has the well-known problem that during forming the emulsion by mixing and stirring the nematic crystal and the polymer, the liquid crystal particles are not distributed uniformly in the emulsion and the layer of liquid crystal particles are not present as a layer of uniform thickness.
Other means exist for generating polymer-surrounded nematic droplets that result in similar electro-optical films. One method is to microencapsulate the emulsified nematic droplets with the polymer shell immediately after forming the emulsions microcapsulated, and then to suspend these encapsulated droplets in some binder material to form a film. In another method, a mixture of nematic liquid crystal and a prepolymer is made to form the uniform liquid crystal particle with a coated film. However, these methods have disadvantages of causing the complex processes.